Thumb Carpometacarpal (CMC) Grind Test

The Thumb Carpometacarpal (CMC) Grind Test is a commonly used clinical examination to evaluate the integrity of the thumb’s CMC joint and to detect basal joint osteoarthritis. A positive test indicates arthrosis or synovitis, typically characterized by pain and crepitus (joint grinding) in the CMC joint [1].

This test is particularly useful when there is suspicion of degenerative changes in the thumb’s basal joint – a frequent cause of pain, reduced grip, and functional limitations in daily hand use.

Test procedure

Patient positioning

• The patient is seated or standing with a relaxed hand and wrist.

Test execution

• The examiner stabilizes the first metacarpal bone of the thumb.

• The thumb’s CMC joint is rotated in a circular motion, while applying mild axial compression.

• The movement is intended to mimic a grinding effect, stressing the articular cartilage of the joint [4].

Interpretation

• Positive test: sudden, sharp pain in the CMC joint, often accompanied by crepitus → suggests joint arthrosis or synovitis [5].

• Negative test: no pain or crepitus is present.

Alternative clinical tests

Other manual tests may provide complementary diagnostic information for CMC joint pathology:

• Crank Test → evaluates joint congruence and translational laxity.

• Distraction Test → reproduction of pain suggests inflammatory joint involvement.

• Volar Compression Test → useful for identifying early inflammatory changes in the base of the first metacarpal.

• Pressure-shear and Lever Tests → potentially more clinically accurate for diagnosing CMC osteoarthritis [2,3].

Diagnostic validity and evidence

Several studies have assessed the diagnostic accuracy of the Thumb CMC Grind Test:

Author	Sensitivity (%)	Specificity (%)
Merritt et al.	42	80
Merritt et al.	53	93
Choa et al.	30	96.7

• High specificity → the test is reliable for confirming CMC osteoarthritis when positive.

• Low sensitivity → a negative test does not necessarily exclude the condition [5].

Clinical relevance

• The Thumb CMC Grind Test is a fast and easy clinical assessment for basal joint osteoarthritis.

• Because of its high specificity, a positive result is strongly indicative of pathology.

• However, due to low sensitivity, it should not be used in isolation.

• The test is best combined with other manual assessments and imaging modalities (e.g., X-ray or MRI) to establish an accurate diagnosis.

Conclusion

The Thumb CMC Grind Test is a simple, reliable, and specific examination tool to diagnose basal thumb osteoarthritis. While a positive test strongly suggests joint arthrosis, a negative test cannot rule it out. For best clinical accuracy, it should be used alongside other manual tests and imaging investigations.

References

1. Colditz JC, Koekebakker N. (2010) A New Splint Design for the Thumb CMC Joint [White Paper] published by Nea International bv / Push Braces, Maastricht-Airport, the Netherlands, www.push.eu

2. Sela Y, Seftchick J, Wang WL, Baratz ME. The diagnostic clinical value of thumb metacarpal grind, pressure-shear, flexion, and extension tests for carpometacarpal osteoarthritis. J Hand Ther. 2019 Jan-Mar;32(1):35-40.

3. Model Z, Liu AY, Kang L, Wolfe SW, Burket JC, Lee SK. Evaluation of Physical Examination Tests for Thumb Basal Joint Osteoarthritis. Hand (N Y). 2016 Mar;11(1):108-12.

4. https://medisavvy.com/thumb-grind-test/ accessed online October 17th, 2017

5. Model, Z., Liu, A. Y., Kang, L., Wolfe, S. W., Burket, J. C., & Lee, S. K. (2016). Evaluation of Physical Examination Tests for Thumb Basal Joint Osteoarthritis. Hand (New York, N.Y.), 11(1), 108–112. http://doi.org/10.1177/1558944715616951